Wireless communications services are expanding rapidly into an ever-wider array of communications media. WiFi or wireless fidelity systems, for example, are now commonplace and being used in a variety of commercial and public settings, such as homes, offices, shops, malls, libraries, airports, and the like. Wireless distribution systems, in some applications referred to as “distributed antenna systems”, or “DAS”, are commonly used to improve coverage and performance of WiFi communication systems. Such systems typically include a plurality of spatially separated antennas, and communicate with a variety of such commercial communications systems to distribute their services to clients.
One approach to deploying a wireless distribution system involves deployment in a location of multiple radio frequency (RF) antenna coverage areas, such as multiple access points, also referred to as “antenna coverage areas.” Combining a number of access point devices creates an array of antenna coverage areas within the location. Because each of the antenna coverage areas covers a small area, there are typically only a few users (clients) per antenna coverage area.” This minimizes the amount of RF bandwidth shared among the wireless system users.
FIG. 1 illustrates distribution of communications services to coverage areas 10(1)-10(N) of a wireless distribution system 12, where ‘N’ is the number of coverage areas. These communications services include cellular services, wireless services such as RFID tracking, Wireless Fidelity (WiFi), local area network (LAN), WLAN, and combinations thereof. The coverage areas 10(1)-10(N) are remotely located, and created by and centered on remote access units 14(1)-14(N) connected to a central unit 16. The central unit 16 is communicatively coupled to a base station 18. If the wireless distribution system 12 is a broadband wireless distribution system, the central unit 16 receives downlink communications signals 20D in multiple frequency bands for different communications services from the base station 18 to be distributed to the remote access units 14(1)-14(N). The remote access units 14(1)-14(N) receive downlink communications signals 20D from the central unit 16 over a communications medium 22 to be distributed as downlink communications signals 20D to the respective coverage areas 10(1)-10(N). Each remote access unit 14(1)-14(N) may include an RF transmitter/receiver and a respective antenna component 24(1)-24(N) connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 26 within their respective coverage areas 10(1)-10(N).
The remote access units 14(1)-14(N) in the wireless distribution system 12 are also configured to receive uplink communications signals 20U in multiple frequency bands from the client devices 26 in their respective coverage areas 10(1)-10(N). The uplink communications signals 20U are routed to different uplink path circuits (not shown) in the remote access units 14(1)-14(N) related to their frequency band. At the related uplink path circuits in the remote access units 14(1)-14(N), the uplink communications signals 20U are filtered, amplified, and combined together into the combined uplink communications signals 20U to be distributed to the central unit 16. The central unit 16 separates out the received combined uplink communications signals 20U into their respective bands to distribute to the base station 18.
Interference of downlink communications signals 20D and/or uplink communications signals 20U may occur in the wireless distribution system 12 due to non-linear signal processing components provided therein. For example, in the broadband wireless distribution system 12 in FIG. 1, signals in a frequency band of a given downlink communications signal 20D received and processed by a non-linear signal processing component in the central unit 16 is duplicated as harmonics in other frequency bands falling within frequency bands of other received downlink communications signals 20D.
FIG. 2 is a partial schematic of an access unit 14 having an antenna component 24 connected to a base unit 32 by a coaxial cable 34. The access unit 14 has a conventional antenna connectivity monitoring circuit on a printed circuit board (PCB) 38. The base unit 32, by way of the cable 34, provides DC power and RF communications signals to the antenna component 24. A resistor 40 and resistors 42, 44 form a voltage divider in which the voltage between resistors 42, 44 is detected by an analog-to-digital converter (ADC) 54, and is converted to a digital representation of the voltage. An RF blocking inductor 50 blocks or “chokes” RF frequencies from reaching the ADC 54. The digital connectivity indicator voltage from the ADC 54 is provided to a controller 56. If the cable 34 connecting the antenna component 24 to the base unit 32 is disconnected, the voltage between resistors 42, 44 increases, and the ADC 54 converts the new voltage to digital format and provides it to the controller 56. The controller 56 uses that digital signal to determine that the antenna component 24 is disconnected.
The monitoring circuit of FIG. 2 is shown as integrated on the PCB 38, and the antenna connects directly to components of the PCB 38.